Certain thermoplastic elastomers do not require a vulcanization process in their production, yet they still exhibit rubber elasticity. Such thermoplastic elastomers are used to form stretch materials such as films, bands, strands, and non-woven fabrics, which are then used in combination with laterally expandable non-woven fabrics or pleated non-woven fabrics to form stretchable articles. These stretch materials or articles have become widely used in various sanitary products such as disposable diapers, toilet training pants, and medical products such as surgical bandages and surgical gowns. Traditionally, thermoplastic polyurethane elastomers or hydrogenated styrene-based thermoplastic elastomers have been used in these applications.
In order for these stretch materials to be used in the aforementioned applications, they must have properties such as a high flexibility to reduce the irritation and pressure that the materials can exert on a human body, a good stretchability, a good stress relaxation property to reduce residual strain, and a good processability. None of conventional thermoplastic elastomers are less than satisfactory in terms of their quality and processability, however.
For example, thermoplastic polyurethane elastomers, though highly stretchable, lack required flexibility and are also unfavorable in terms of water-resistance and weather-resistance. Likewise, hydrogenated styrene-based thermoplastic elastomers have poor processability despite their relatively high weather-resistance, flexibility, and stretchability.
In view of these drawbacks of conventional stretch materials, it is an objective of the present invention to provide a stretch material made of a thermoplastic elastomer that has a good stress relaxation property, bears less residual strain, and at the same time exhibits a stretchability and a flexibility comparable to vulcanized rubber. Such a stretch material can be stretched easily to better fit a human body without causing undesired irritation or exerting undesired pressure on the human body. Furthermore, the stretch material exhibits a good melt-processability during high-speed production and is thus easy to produce.